Is exacerbated pain when chewing or eating acidic foods a characteristic symptom of mumps? Why does this happen?

Yes, this description is very accurate. The intensification of pain when chewing or ingesting acidic foods is arguably a hallmark symptom of mumps. Many individuals only realize they might have mumps due to this very phenomenon.

Why does this happen?

To understand this, we need to start with how our saliva is produced.

You can imagine our parotid gland as a small factory that produces "spit" (which is saliva). This factory has a duct (the parotid duct) that leads into our mouth.

The Brain's "Rush Order": When we see, smell, or eat food, our brain signals this "saliva factory": "Time to work! Prepare for digestion!" This signal becomes particularly intense when we consume acidic foods like lemons, hawthorn, or vinegar. The brain perceives it as, "Whoa, something strong is coming; a lot of saliva is needed to neutralize it." Consequently, it sends a "rush order" to the factory, demanding immediate and copious saliva production.
The Inflamed Factory's "Distress": When you have mumps, this "saliva factory" itself is in an "inflamed, swollen, and painful" state. It's like an already injured, swollen, and aching muscle that's "on strike" and trying to rest.
Forced Operation Causes Intense Pain: At this crucial moment, as soon as you eat something sour, the brain's "rush order" comes in. This already fragile and compromised factory is forced to contract violently and desperately push out saliva. This sudden, forceful contraction and abrupt increase in internal pressure severely irritate the already inflamed glandular tissue, triggering a very distinct and sharp pain.

To use a simple analogy:

Imagine you have a severe bruise on your arm. Normally, if you don't move it, it might just have a dull ache. But if you're forced to use that muscle to quickly lift a heavy object, that sudden exertion will undoubtedly make you cry out in pain.

Eating sour foods has the same effect on an inflamed parotid gland. This phenomenon is medically referred to as "gustatory-salivary reflex pain" and serves as a significant diagnostic indicator for doctors when assessing mumps.